1. Field of the Invention
The present invention relates to an engine including an exhaust sensor that detects a state of exhaust gases flowing in an exhaust passage, and an outboard motor including the engine.
2. Description of the Related Art
US 2014/0322997 A1 discloses an outboard motor powered by a V-type engine. This outboard motor is equipped with an in-bank exhaust system that discharges exhaust gases to the inside of two cylinder banks.
The engine includes an exhaust pipe that returns exhaust gases discharged from exhaust manifolds to the exhaust manifolds. Exhaust gases discharged from the two cylinder banks are collected in the exhaust pipe and purified by one catalyst disposed inside of the exhaust pipe. Two exhaust sensors are disposed upstream and downstream of the catalyst, respectively. A water jacket that guides cooling water is provided between an inner wall surface of the exhaust pipe that defines an exhaust passage and an outer wall surface of the exhaust pipe.
When an output of the engine is low (for example, during idling), a temperature of the inner wall surface of the exhaust passage may drop to a temperature equal to or lower than the dew point. In this case, moisture contained in the exhaust gases changes into liquid droplets on the inner wall surface due to condensation. This condensed water flows inside of the exhaust passage along the inner wall surface. When the condensed water comes into contact with the exhaust sensor, the exhaust sensor may malfunction.
Further, in an engine for an outboard motor, rather than a system that circulates cooling water, a system that takes water from outside a vessel into the inside is generally used so that cooling water having low temperature is reliably supplied. Therefore, as compared with an engine for a land vehicle, the temperature of the inner wall surface is low, and condensed water is easily generated.